1. Field of the Invention
The present invention relates to a sensor module having a housing in which a micromechanical sensor is disposed.
2. Description of Related Art
Micromechanical sensors are used in many technical applications. Thus, sensor modules featuring micromechanically manufactured rotation rate sensors or acceleration sensors for determining the current state of motion of a motor vehicle are used in the automotive sector, for example. In such a sensor module, a micromechanically manufactured sensor chip is accommodated in a sensor housing. In this context, the so-called mold housing is a relatively frequently used housing form, in which the sensor chip is embedded in a protective layer made of a plastic mass, for example. To this end, the sensor chip is mounted on a circuit board substrate and sprayed with a suitable molding material. As a rule, the sensor module is made in a so-called multiple printed panel along with additional sensor modules. The finished modules are subsequently separated. This is usually done by sawing. Due to the structure, the contacts of the sensor housing are disposed only on the bottom side.
In a mold housing, mechanical stress occurs on the micromechanical and electronic circuit structures of the sensor chip embedded therein, in particular in the event of temperature differences. This is caused primarily by different properties of the materials used, such as different expansion coefficients among the circuit board substrate and the plastic material. Mechanical stresses may also be induced within the mold housing during its production, however.
The mechanical stress on the sensor chip and on the evaluation circuit may have a negative effect on the sensor characteristic. In unfavorable cases, the mechanical stress in the mold housing may even result in the destruction of the sensors. For example, in the event of mechanical stresses, the sealed glass connection between the sensor chip and an additionally used cap may delaminate.
In order to avoid malfunctions caused by stress, sensors that are particularly mechanically sensitive, such as low-g sensors or rotation rate sensors, are not packaged in the cost-effective mold housing. Instead, more expensive ceramic substrates or premold housings are used for these sensors.